Method of making supply cathodes and supply cathodes manufactured by means of these methods



March 26, 1957 H. .1. LEMMENS 2,786,259

METHOD OF MAKING SUPPLY CATHODES AND SUPPLY CATHODES MANUFACTURED BY MEANS OF THESE METHODS Filed Nov. 7, 1951 INVENTOR Hendri kus Johannes Lemmen By Ageni United States Patent 2,786,259 METHOD OF MAKING SUPPLY CATHODES AND SUPPLY CATHODES hiANUFACTURED BY MEANS OF THESE METHODS Hendrikus Johannes Lemmens, Eindhoven, Netherlands, assignor, by mesne assignments, to North American Philips Company, Inc., New York, N. Y., a corporation of Delaware Application November 7, 1951, Serial No. 255,243

Claims priority, application Netherlands November 18, 1950 1 Claim. (Cl. 2925.14)

This invention relates to methods of making supply cathodes, in which a part of the wall of the cathode body is constituted by a member of tungsten, molybdenum, tantalum, hafnium or niobium sintered to porosity at a high temperature, the joint between this porous member and the remaining metal part of the cathode being such as to form a supply chamber which contains alkaline earth metal compounds and in which the pores of the porous member constitute the largest openings. Furthermore the invention relates to cathodes manufactured by means of this method.

The aforesaid cathodes have long and high emission. The part of the cathode wall not constituted by the porous member preferably consists of molybdenum.

When using mass-production methods for manufacturing the non-porous part of the supply chamber, this cathode part is easily contaminated, so that the emission of the cathode is adversely affected and more particularly the cathode-formation takes an extremely long time.

In a method of making cathodes with which part of the wall of the cathode body is constituted by a porous member of tungsten, molybdenum, tantalum, hafnium or niobium, sintered to porosity at a high temperature which is joined to the remaining metal part of the cathode so as to form a supply chamber containing alkaline earth metal compounds, the non-porous wall part of the supply chamber is, according to the invention, pickled prior to joining it to the porous part so that the impurities are removed.

The pickling operation may be carried out chemically and after that it is advisable to anneal the part in question in hydrogen. Preferably, however, recourse is bad to electrolytic pickling which has the advantage that after rinsing and drying no further after-treatment is required.

In order that the invention may be readily carried into efiect, an example will now be described in detail with reference to the accompanying drawing.

The sole figure shows a supply cathode, the reference numeral 1 denoting a tungsten plate sintered to porosity, 2 denoting a cylindrical molybdenum case whose bottom 3 is indented so that this bottom together with the tungsten plate welded to the edge of the molybdenum case forms a chamber containing a barium-strontium carbonate pastille 4, a heater helix 5 completing the cathode. For joining the parts 2, 1 and 4 the bottom 3 is pickled externally. A chemical pickling bath may, for example, be composed of three parts sulphuric acid of one part concentrated nitric acid and one part water. The pickling operation is followed by rinsing, drying and annealing in hydrogen at 1100 C. As an alternative, the bottom 3 may be pickled electrolytically in a bath containing 4 parts sulphuric acid of 70% and one part concentrated phosphoric acid, the current strength being 0.25 to l a./mm.

After formation, cathodes made by means of the aforesaid methods have practically no deposit at the inner side of the porous member, the barium-strontium oxide being a light grey. In the presence of impurities there is a dark deposit and the barium-strontium oxide is also dark coloured.

What I claim is:

In the method of making a cathode constituted by a non-porous body of refractory metal forming an internal cavity in which a supply of heat-decomposable alkaline earth compounds is disposed, said cavity being closed by a porous wall member of refractory metal, the pores of which constitute the largest apertures connecting the cavity to an electron-emissive surface of the cathode, the steps immersing the non-porous body in an electrolytic bath consisting of four parts sulphuric acid of 70% concentration and one part concentrated phosphoric acid while passing a current of about 0.25 to l amp/cm. through said bath to remove impurities from said body, and welding said non-porous body to said porous member.

References Cited in the file of this patent UNITED STATES PATENTS 1,253,906 Sutter Jan. 15, 1918 2,447,038 Spencer Aug. 17, 1948 2,460,739 Francis Feb. 1, 1949 2,542,779 Neill Feb. 20, 1951 2,624,024 Jansen et al. Dec. 30, 1952 2,688,709 Knockel et al. Sept. 7, 1954 OTHER REFERENCES Welding Handbook, American Welding Society, 3rd edition, 1950, pages 376-378. (Copy in Div. 14.) 

